Over the recent years, a technology called WiMAX (Worldwide Interoperability for Microwave Access) has been focused as one of wireless communication technologies. The WiMAX is the technology developed as a technique of configuring Wireless MAN (Metropolitan Area Network) by wirelesslizing the MAN in place of a telephone line and an optical fibre line. The MAN is defined as a wide area network which mutually connects LANs (Local Area Networks) in the metropolitan areas and specified local areas by enabling a wireless connection between a common carrier and a user's home to be established. The WiMAX is said to enable one single wireless base station to cover an area extending 50 km in radius at a transmission speed of approximately 70 Mbps at the maximum.
At the present time, the IEEE (Institute of Electrical and Electronic Engineers) standardizes, e.g., Non-Patent document 1 as the WiMAX oriented to fixed terminals and the WiMAX oriented to mobile terminals.
In the wireless communication system such as the WiMAX, normally the communications are performed between the wireless base station connected via a wired link to a high-order network and a wireless terminal (which will hereinafter be also simply termed a [terminal]). Further, the wireless communication system such as the WiMAX introduces a relay station which wirelessly performs relay-forwarding between the wireless base station and the terminal, thereby enabling the communication area to be expanded and a communication throughput of the terminal to be improved.
FIG. 1 is a view depicting an outline of the wireless communication system in the case of carrying out mobile-oriented wireless relay communications.
The wireless communication system illustrated in FIG. 1 is configured by including a wireless base station (BS: Base Station), a relay station (RS: Relay Station) and a terminal (MS: Mobile Station). In the example of FIG. 1, four mobile stations MS1-MS4 exist. The mobile stations MS1 and MS2 are located in an area enabling the MS1, MS2 to perform direct communications with the base station BS. Further, the mobile stations MS3 and MS4 are located in an area enabling the MS3, MS4 to perform the communications with the base station BS via the relay station RS. The base station BS is connected to a high-order network (unillustrated) and forwards pieces of data, which are transmitted and received by the mobile stations MS1-MS4, to the high-order network.
The mobile stations MS1 and MS2 perform the communications with the base station BS by transmitting and receiving radio signals directly to and from the base station BS. The mobile stations MS3 and MS4 transmit and receive the radio signals to and from the relay station RS, and the relay station RS serving as a proxy station of the mobile station MS3 or MS4 transmits and receives the radio signals to and from the base station BS, thus performing the communications. The relay station RS operates (behaves) as if appearing equal to the mobile station when viewed from the base station BS. Further, the relay station RS operates as if appearing equal to the base station BS when viewed from the mobile stations MS3 and MS4. The relay station RS temporarily receives the radio signals transmitted by the base station BS or the mobile stations MS3, MS4, and relay-forwards the radio signals for the sake of the mobile stations MS3 and MS4 or the base station BS by executing necessary processes.
The standardization of this type of relay communication method in the mobile-oriented wireless communication system is currently underway as Multi-hop Relay (MR) according to IEE802.16j. For example, Non-Patent document 2 is opened to the public as Draft Standard according to IEE802.16j.    [Patent document 1] Japanese Patent Laid-Open Publication No. 2005-252677    [Patent document 2] Japanese Patent Laid-Open Publication No. 2003-258719    [Patent document 3] Japanese Patent Laid-Open Publication No. 2006-196985    [Non-Patent document 1] IEEE Standard 802.16e-2005 AND 802.16-2004/Cor1-2005 (2006-2-28)    [Non-Patent document 2] IEEE P802.16j/D1 (2007-08-08)